Earlier work with rats and our recent human studies demonstrate that oral exposure to dietary fats alters fat metabolism. Four studies are proposed to more fully characterize this phenomenon so that its physiological and public health significance can be established. Generally, these protocols will entail within-subject designs. The procedures will involve subjects ingesting a load of fat (as a milkshake or in capsules) and then receiving various forms of oral stimulation. Blood samples will be collected at timed intervals for analysis of metabolic responses to the oral stimulation. In one study, the type of lipid contained in the fat load will be manipulated (saturated versus unsaturated, long-chained versus medium-chained) to assess the effects of fat type on the response. In another study, the form of oral stimulation will be altered to include fat substitutes composed of protein, carbohydrate or fat. This will help to identify the effective stimulus for the effect. The third study will have subjects ingest the load as a milkshake (as is routinely done in fat challenge tests) with and without pleasant (sweet) and less pleasant (bitter) tastes to examine the role of taste in reported augmented postprandial triglyceride levels in trials where sucrose or fructose are added to the lipid load. The fourth study will be conducted with individuals who have normal and elevated basal plasma triglyceride concentrations. There are preliminary reports of greater postprandial trigylceride excursions among individuals with high basal triglyceride levels. Given that postprandial lipid levels may be related to coronary heart disease risk, it is important to understand the factors that influence lipid metabolism. Oral factors are especially important with the increasing use of products containing compounds that mimic the sensory properties of fats.